This invention relates to a xerographic copying apparatus. Such an apparatus includes an optical system for forming an optical image of an object to be copied on an electrically charged photoconductive surface, the optical image forming a corresponding electrostatic latent image on the surface, and means to develop the latent image with a particulate toner material.
The particulate toner material used in a xerographic copying machine to develop the electrostatic latent image is usually a fine black powder which, unless carefully confined within the machine, can deposit on various components of the machine, with deleterious effect. In particular, the ingress of toner into the optical system gives rise to the deposition of toner on the optical surfaces of lenses and mirrors, with consequent degredation of image quality.
Although it is not usually possible to provide a sealed optical system, i.e. one in which the major optical components are within a totally sealed compartment, it is possible to form a substantially closed compartment containing the major optical components. In this way, the ingress of toner may be kept to a low level.